Running around on the playground will boost a kid's performance in the classroom, according to Spanish researchers.

Running around on the playground will boost a kid's performance in the classroom, according to Spanish researchers who believe they've uncovered a connection between children's physical fitness and their school grades.

An investigation led by a University of Granada team suggests a link between a child's aerobic capacity (their cardiovascular fitness) and motor ability (their speed and agility) and a greater volume of grey matter in brain regions associated with learning and organisation.

"Our work aims at answering questions such as whether the brain of children with better physical fitness is different from that of children with worse physical fitness and if this affects their academic performance," said study co-author Francisco B. Ortega, from the University of Granada's faculty of sport sciences, in a statement.

"The answer is short and forceful: yes, physical fitness in children is linked in a direct way to important brain structure differences, and such differences are reflected in the children's academic performance."

The study, published in the journal NeuroImage, didn't find a link between muscular fitness and greater brain volume.

Irene Esteban-Cornejo, the study's lead author, said the research suggests a simple way to boost a child's smarts.

"Physical fitness is a factor that can be modified through physical exercise," she said. "Combining exercises that improve the aerobic capacity and the motor ability would be an effective approach to stimulate brain development and academic performance in overweight/obese children."